The invention relates to a display device comprising an electro-optical material between a first substrate and a second, substantially parallel substrate, in a space bounded by a sealing edge, said first substrate being provided with electrodes and a color filter which is covered with a protective layer only within the space bounded by the sealing edge.
Such display devices are well known and are used, for example, in monitors, television receivers and display devices for motor cars, telephone equipment and instruments.
A display device of the type mentioned in the opening paragraph is described in U.S. Pat. No. 5,157,527 (PHN 13.252). In said display device a description is given of the manner in which a color filter on a first substrate is covered with a protective layer, the so-called top coat, which is situated within the space bounded by the sealing edge. Such a patterned top coat is provided, for example, by flexographic printing and has a number of advantages over a top coat applied by `spinning`. In the latter method (spinning), the top coat extends underneath the sealing edge, so that this sealing edge is not bonded directly on to the substrate (or on to an electrode provided thereon), but on to the top coat (or on to an electrode provided thereon), which in turn is bonded on to the substrate. This double bond adversely affects the reliability of the seal. The same drawbacks arise when drive circuits (ICs) supplying drive voltages, as in the case of so called passive matrices in particular, are connected to said electrodes, or when two-pole switching elements are used for driving.
In addition, the material used for the top coat is often permeable to moisture, so that moisture coming from outside penetrates the display device.
Finally, the printing method is cheaper than spinning because, among other things, the material is less expensive.
A drawback of the printing method occurs when, in order to increase the contrast, the color filter is provided with a layer of an opaque material (black matrix), which is composed entirely or partly of a conductive material. To preclude that electrodes extending beyond the edge of the top coat electrically contact the black matrix (and consequently are mutually short-circuited), said top coat must extend beyond the color filter, including the black matrix (while allowing a given tolerance). As a result, a part of the useful surface is lost at the edge of the effective display section, so that the effective display section is reduced in size.